Arc prevention system



Oct. 9, 1951 P. M. c. TOULON ARC PREVENTION SYSTEM 2 Sheets-Sheet 1Filed Aug. 4, 1947 NON DaFDO WFON E: m j m2 H EN 2m 2m mom 1 wONINVENTOR PIERRE MARIE GABRIEL TOULON ATTORNEY Patented Oct. 9, 1951 ARCPREVENTION SYSTEM Pierre Marie Gabriel Toulon, Paris, France, as-

signor to Products & Licensing Corporation, New York, N. Y., acorporation of Delaware Application August 4, 1947, Serial No. 766,037In France January 8, 1946 Section 1, Public Law 690, August 8, 1946Patent expires January 8, 1966 13 Claims. 1

The present invention relates generally to a system for accomplishingsparkless commutation of electric currents, and more particularly tosystems for making and breaking electric circuits, which may operate athigh voltages and current intensities, without destructive sparking. Theinvention finds application in accomplishing sparkless commutation inrotary rectifiers and converters of the type which accomplish rapidcommutation of circuits by means of mechanical circuit makers andbreakers, or commutators, but the invention is not limited to such uses,and finds general application wherever a circuit must be opened, orclosed, or opened and closed, or vice versa, in rapid succession.

It is a well known fact that commutation of electric current ofconsiderable magnitude, and more particularly where high voltages areinvolved, presents problems of exceptional difficulty, because thesparking consequent on normal commutation efiects rapid wear anddestruction of the conductive contacts utilized to effect thecommutation.

I have observed that the difliculties encountered in commutation are dueto two primary phenomena. When a circuit is being closed by bringinginto contact two metallic or other conductive contacts, the contactsbecome separated by a very small distance during the act of closure,

and while separated by such a small distance, a

high voltage exists between the contacts. The contacts are separated byair, or by some other gaseous dielectric, which is disrupted in responseto the high voltage existing between the contacts, so that a small sparkoccurs between the contacts. If the current intensity in the spark issufficiently great, intense ionization of the gaseous dielectric iscaused, particularly if the contacts are subjected to local heating bythe spark, and a disruptive arc discharge is initiated. This disruptivearc discharge is extremely destructive, especially if of considerableduration.

During opening of the contacts, the cross-section of the contacts whichremain in contact during the opening process is progressively reduced,so that the current density in the contacts is correspondinglyincreased.- This current density becomes so high, eventually, that somevolatilization of the material of the contacts occurs, and someionization of the gaseous dielectric adjacent to the contacts, so thateventually arc discharge is produced. This arc discharge is destructiveof the contacts, and the destruction accomplished is higher the higherthe current intensity. and he limit?! the em ils 01? he 9. 72:

In order to overcome the above recited. difiiculties, I make use of anauxiliary electric generator, using that word very broadly as implyingany device in which a voltage may be generated. I connect the auxiliaryelectric generator in series with the circuit to be commutated, and I sodesign the auxiliary electric generator that it is capable of generatingan instantaneous electric voltage sufficiently great to counter-balanceany potential difference existing between a pair of contacts which areabout to come together to close an electric circuit, and I so select thepolarity of that generator as to counter-balance that potentialdifference, thus bringing to zero, at the moment of contact, the totalvoltage existing in the circuit. Thereby, current flow in the circuit isreduced to zero at the moment of contact, and circuit closure isaccomplished without sparking or disruptive discharge of any charactenIn the case of circuit opening the generated voltage reduces currentflow across the contacts to zero, by reducing the voltage across thecontacts to zero, or counterbalancing any voltage there existing.

Accomplishment of the process outlined in the previous paragraphinvolves the following steps or provision for accomplishing thefollowing functions. In the first place it is necessary to measure thedifference of potential which exists between a pair of contacts justprior to their coming into contact. In the second place I must providemeans for measuring the intensity of current flowin between thecontacts, precisely at the instant of their separation. I must provide alocal electrical generator, which is capable of providing a variable andcontrollable electromotive force over a period of time, and which isconnected in series with the contacts which are to be separated orclosed. I must further provide devices for controlling the localgenerator, for inserting in the circuit being commutated an appropriatevoltage, of the precise magnitude and sense required forcounter-balancing the voltage existing between the contacts immediatelyprior to their closure, and for cancelling current flow in the contactsimmediately prior to their opening.

Briefly described, and in accordance with the preferred embodiment ofthe present invention, the local generator may take the form of anelectric valve, having an appropriate energizing means, output circuit,and input circuit. The desired voltages for insertion in the commutatedcircuit may be generated in the output circuit of the electronic valve,in response to control signals applied to its input circuit. Morespecifically the electronic valve may be constituted of a triode, thecontrol grid which may be provided with control voltages of transientnature, during closure or-opening of the commutating contacts, and theoutput circuit of which may comprise a transformer having a secondarywinding connected in series with the circuit to be commutated, and aprimary winding connected in series with the anode of the triode.

Voltages applied to the control electrode of the triode may be derivedfrom impedances connected with the circuit to be commutated, viafeed-back amplifiers. Accordingly, the triode forms one element of afeed-back loop, having both its starting and terminating points in thecircuit to be commutated, and the loop is. designed to be stronglydegenerative, so that any condition found at the input of the loop tendsto be annulled via the output of the loop.

My inventiongfindsparticular application to rotary commutators', inwhich case the circuits to be ma-de and closed may be those between thecopper segments of the commutator, and brushes, which may be metallic,but which if desired may be fabricated of other conductive material suchascarb n- I have found in practice that the principles of the presentinvention may be applied to rotary converter construction, where thevoltages in- 1 volved are of the order-of several hundred kilovolts, andwherein the powers to be oommutated ar of the order of several hundredthousand kilo-watts. v e

The present system has been found efiective in practice, for extremelyhigh potentials existent between adjacent segments of the commutator,for commutating power of extremely high orders, and regardless of thevariations of load which ma ex st n t e 'comm ta e C r u T ve tion isextremely flexible in application, having been found extremely valuablefor wide ranges of frequencies, regardless of the power-factor of theenergy which must be commutated, regardlessfof the number ofinterruptions which occur perflsecond, and regardless of the mod ofcommutation, i. e., whethe in response to rotating brushes andfixedcommutator segments, or vice versa, and regardless of thespeed ofcommutation.

It is accordingly a broad object of the present invention to provideanove'l system of sparkless com tat It is, a mor specific object of theinvention to provide a system for annulling the difierence of voltageexisting between a pair of contacts in process of closing,

.It is anothcrobject of the invention to provide a system of commutationwherein the current flow, between a pair of contacts in process ofopening is annulled.

Still another, object of theinvention resides in the provision of asystem of commutation wherein the voltage betweena pair of contacts inprocess of, closing is annulled during the closing process, and whereinthe current flow between these contacts at the moment of opening is alsoannulled.

It is a more specific object of the present invention to provide asystem of sparkless commutation wherein voltage across a pair ofcontacts is annulled while the contacts are closing and wherein currentflow between the contacts is annulled while the contacts are opening,and wherein the annullment of both voltage and current is accomplishedby means of a degenerative feedback loop having both an input and anoutput connected in the circuit being commutated, and in series with thecontacts.

Still another object of the present invention resides in the provisionof a system for continually measuring the voltage existent across a pairof contacts in process of closing, and the current flowing between apair of contacts in process of opening, for utilizing these measurementsto introduce into the circuit containing the contacts an opposingvoltage sufiicient in magnitude at all instants of time, and of properpolarity, to counter-balance the measured voltage, and to annul the flowof current.

The above and still further features, objects, and advantages of theinvention will become apparent upon consideration of the following"detailed disclosure of a specific embodiment thereof, especially whentaken in conjunction with the accompanying drawings, wherein:

Figure 1 isa schematic circuit-diagram .of a preferred embodiment of theinvention; and

Figure 2 is a timing diagramshowing various conditions of voltage andcurrent existing in a circuit subject to closure and opening, in as:cordanoe with the invention.

Referring now more specifically to the ac.- companying drawings, thereference numeral 26! indicates an input circuit, which provides powerto be commutated, and then to be delivered to an output circuit 262. Theinput circuit 2M may, for example, be an alternating' current circuit,and the output circuit 202 a D. C. circuitythe function of thecommutation being to rectify the alternating current, and to deliver tothe output circuit 262 a rectified direct current. On the other hand,the invention is by no means limited to this application, and ma beapplied, for example, to the conversion of frequency, in which case theoutput circuit 2H2 may be a load circuit for the input Zlll, wherein"flows current of alternating nature, at a1 different frequency thanflows in the input am. The invention also finds application to theconversion of direct current into alternating current, in which case theinput circuit may be a D. C. circuit and the output circuit an A. C.circuit, conversion being accomplished by means of the commutationprocess.

Commutation is accomplished by means of a brush 283, assumed to berotating with respect to a commutator segment 254, Rotation of the brushmay be accomplished in response to rota tion of a motor 285, which isenergized from a source of power conventionally illustrated as a battery229, when the switch 22! is closed. Suitable means are provided, whichare not illustrated in order that the circuit diagram may not be undulycomplicated, and in order better to illustrate the basic principle ofthe invention, for bringing the brush 203 into contact with thecommutator segment 20% precisely at the time assigned for closure of thecircuit between the input 20! and the output 292, and for providing thatthe brush 2% will leave the segment 204 at the time assigned for openingof the circuit.

The problem presented is, then, that of annulling the voltage existingbetween the brush 203 and the commutator segment 2% just as theseelements come into contact, and for annulling current flow between thecommutator segments 203,204, just as these elements break circuit,- andthis regardless of the precise con tent of the voltage or current, or oftheir variations with time, or of the speed of relative motions of thebrush 203 and the commutator 204.

In accordance with the invention, I connect in series with the brush 203a resistance 205 and a winding or coil 201, the latter constituting thesecondary winding of a transformer having a primary winding 208. Thevoltage across the resistance .206 is then a precise replica of thecurrent flowing in the commutated circuit.

I further provide an auxiliary commutator segment 214 and an associatedbrush 215, the commutator segment 214 being connected direct- 1y to thecommutator segment 204, and the brush 215 being driven in synchronismwith the brush 203 by the motor 205, except for a small relative angulardisplacement between the brushes 203 and 215, the brush 215 beingslightly in advance, so that the brush 215 comes into contact with thesegment 214 slightly before the brush 203 comes into contact with thesegment 204. In series with the brush 215 is connected two highresistances in series, designated by the reference numerals 210 and 211,values being selected sufficiently high to permit the passage of currentof very low intensity only, in order that no spark formation may bepermitted between the brush 215 and the segment 214, and further inorder that the voltage across the resistance 216 shall be a precisereplica of the voltage existing between the brush 215 and the segment214 and consequently between the brush 203 and the segment 204.

The voltage existing across the resistance 203 is applied to the inputof the amplifier 218, while the voltage existing across the resistance216 is applied to the input of the amplifier 219.

There is additionally provided a triode 210, capable of deliveringextremely high power for short intervals of time, triode 210 having inits output or anode circuit the primary winding 208, and having itscathode connected to one output leadof the amplifier 218, and to oneterminal of the resistance 216, the cathode being then considered areference or ground point for the system.

The output of the amplifier 218 is connected to a commutator segment213, while the output of the amplifier 219 is connected to a commutatorsegment 212. A brush, driven in synchronism with the brushes 203 and 215sweeps over these contacts in sequence, being driven by the motor 205.This brush is connected to the control electrode 211 of the triode 210,and consequently applies as a control voltage to that control electrode,in sequence, the outputs of the amplifiers 218 and 219, which arerepresentative respectively of current flowing in the commutated circuitbetween input 201 and output 202, and voltage across the brush andcommutator segment 203, 204, in series with the commutated circuit.

If the time constants of the various parts of the feed-back loop aresufiiciently low, and suitably selected, the reaction of the triode 210is practically instantaneous, and if the amplification provided by theamplifiers 218 and 219 is sufficient, the current flowing in theresistance 206 is reduced to zero, or substantially to zero, as contactbetween the brush 203 and the commutator segment 204 is made, and thecurrent flowing in the resistance 206 is reduced to zero at the timethat the contact between the brush 203 and the commutator segment 204 isbeing broken. To this end the application of control voltage to thetriode 210 from the contacts 212 and 213 is suitably timed, so that thecontact at 212 is connected to the control electrode of the triode 210during the circuit closing time, and so that the contact 213 isconnected to the control electrode of the triode 210 during circuitopening time.

The operation of the present system is now described by reference toFigures 1 and 2 of the accompanying drawings. For the purpose of thisexplanation it is assumed that the following sequence of operationsoccurs. First occurs closure of the contacts 203, 204, between whichexists a predetermined initial voltage V1. Thereafter is accomplishedopening of the contacts 203, 204, in the presence of a current itherebetween. It is a function of the present system to annul thevoltage V1, and the current i, by means of a negative feed-back loop.

The upper horizontal line of Figure 2 illustrates as a timing diagram,the operations which occur in the system starting with an open circuit,and terminating with an open circuit, with an intermediate circuitclosure. It is assumed that at point 23 of the first horizontal line ofFigure 2, open circuit conditions exist, and that the voltage of theinput circuit 201 is not equal to the voltage of the output circuit 202,so that upon making contact between brush 203 and commutator segment 204the risk of starting destructive spark and arc discharge exist. Thevoltage V1 is assumed to be the voltage between the brush 203 andcommutator segment 204 at this instant of time, and is plotted belowpoint 23 on the lowermost line of Figure 2.

Point 24 of Figure 2 corresponds to a time which just precedes closureof the contacts 212, at which time it may be assumed that somepredetermined D. C. current flows in the triode 210.

Point 25 corresponds with the time at which the brush 215 just begins tocontact commutator segment 214, so that the voltage applied to the inputof the amplifier 219 represents the voltage existing between the brush203 and the commutator segment 204, just as circuit closure occurs. Theoutput of the amplifier 219 is now applied via contact 212 to thecontrol electrode of the triode 210, and the negative feed-back loop iseffectively placed in action, to generate a voltage in the secondarywinding 201, which is just adequate to balance out the voltage existingbetween brush 203 and commutator segment 204. At the time 21 the maincontacts 203, 204 close, and shortly thereafter, i. e. at time 28, thecontact 212 is interrupted, breaking the negative feed-back loop. Thelatter remains broken while the contacts 203, 204 are in intimatecontact, and consequently while current is passing between the input 201and the output 202.

The point 29 on the graph represents then a time in an interval whichlasts as long as the circuit is closed. This time is assumed to expireat the point 30, at which time the brush 203 is in process of proceedingout of contact with the commutator segment 204. It is precisely at thistime that the contact 213 is placed in circuit with the controlelectrode of the triode 210, whereby the triode 210 is controlled inresponse to the output of the amplifier 218. which passes a currentdetermined by current flow in the circuit between input 201 and output202, as measured across resistance 20!. Conp at point 33.

is at first at a very low value. increases rather rapidly, so that therate of asvnove nection or contact 2I3 to the control electrode oftriode 2l0} establishes the required feed-back: loop, in readiness foran annulling action, and at point 31 a separation of the contacts 283,29 commences, the contacts being completely broken At point 34, thecontact 2l3 is completely open and the feed-back loop is disestablished.

"Figure 2 may be examined from another point of View. The first line ofthis flgureprovides a time sequence, when certain circuit closureand'opening operations take place. The second line illustrates thevalues, as a time fuction, of the small control current which flows inthe auxiliary contacts 2 I4, 2| 5, and in the resistances 216, 2H, andwhich are representative of voltage between the main commutator contacts203, 204. That current starts at point 25, and it assumes at first ahigh value, due to the high value of the voltage across the contacts283, 29 3. Thereafter, however, due to the negative feedback of voltageintroduced in the secondary winding 207, by the negative feed-back loop,this voltage is reduced radically, and eventually falls substantially tozero when the brush 203 comes into ful contact with the commutatorsegment 204, at point 27.

' The third line of Figure 2 represents the variations as a function oftime of current intensity in the main circuit as measured in terms ofvoltage across the resistance 28%. That current starts only after thecontact between brush 283 and commutator segment 253 1 has beencompleted, i. e. at point 2?, and at time has risen to its maximumvalue, returning some- T7 time thereafter to its normal valuerepresented by 1 'The fourth line of Figure 2 represents variations inoutput current of triode 2H3 as a function of time. is not operative,since the feed-back loop of which it forms a part is not completed.During the period 2 5 to 25, triode current is initiated, and Triodecurrent change of triode current has an appreciable value, the voltageinduced in the secondary winding 20'! being proportionable to this rateof change. The rate of change is so established by the feed-back loopthat the total voltage between brush 203 and commutator segment 204 ismaintained substantially at zero value. When the contacts 212 areopened, however, the variation of current in the feed-back loops ceasesprogressively, so that the eiiect of the feedback loop is destroyed, andthe current flowing between the brush 203 and the commutator segment 204is determined solely by the relation between the input 20! and theoutput 202.

In order to open the main circuit, which be.- gins to occur at the time30, the negative feedback loop is placed in operation via the contactUS, which causes automatically first a rapid increase and then adecrease in current in the triode, i. e. a negative slope for thevariation of current iii This rate of decrease assumes such a value thatthe current in the main circuit falls almost to zero. When the contact2i3 opens entirely, the triode 2H] is removed from the feed-back loop,disabling the latter, which causes the a pearance of a voltage betweenthe brushes 253, 2%.

Prior to time 24, the triode 2W Since, however, this voltage occurs onlyvat an appreciable time after the separation of the contacts, thecontacts have had time to separate sufficiently so that the voltage hasno deleterious effect, is not capable of sparking or arcing, and canremain at any value desired.

The fifth line of Figure 2 represents the voltage generated in thesecondary winding 201, asa function .of time. At the time of contactclosure,

between brush 203 and segment 204, a :voltage appears in the secondarywinding 2'01, signalling that the. negative feed-back loop has commencedaction. This voltage rapidly attains a value such that the voltageexistent between the brush 203 and the contact 20 5 is substantiallyzero, after whichtime the voltage generated in the secondary winding20'! can change .without deleterious effect to the operation of thesystem, even to the extent of change in sign, after time 28. 7 Duringopening of the main circuit, again the voltage suppliedby the negativefeedback loop assumes continuously a value such as to reduce the currentin the main circuit to zero, until the brushes have separated. Afterseparation of the brush 233 and the commutator seg-.- ment 264, thevoltage at the terminals of secondary winding 25'! can assume any valuewhatsoever, but will eventually fall to zero, when the contact 2i3 isbroken, removing the negative feed-back loop from operation.

While I have described and illustrated one specific example of thepresent invention it will be clear to those skilled'in the art thatvariations of the specific arrangement adopted, and of its details, maybe resorted to without departing from the true spirit of the inventionas defined in the appended claims.

What I claim is:

1. A system of sparkiess commutation comprising: means for measuring thepotential existing between two commutating contacts connected in currentcarrying circuit only while said contacts are closing, said contactswhen closed serving to complete said circuit, a feedback amplifierhaving an input circuit and an output circuit, means for applying saidpotential to said input circuit, means for coupling voltage derivingfrom said output circuit in series with said current carrying circuitfor opposing said difierence of potential only while said contacts areclosing, and means for thereafter closing said contacts and for reducingto zero said voltage deriving from said output circuit after saidcontacts have been closed.

2. A system of sparkless commutation comprising: means for measuring thecurrent flowing between a pair of commutating contacts connected in acurrent carrying circuit only while said con.-

tacts are in process oi opening, said contacts when closed serving tocomplete said circuit, a feedback amplifier having an input circuit andan output circuit, means for applying to said in. put circuit apotential proportional to said current flowing between said pair ofcontacts only while said contacts are in process of opening, means forcoupling voltage deriving from said output circuit in series with saidcurrent carrying circuit for reducing said current flowing between saidcommutating contacts, and means for thereafter opening said commutatingcontacts and for reducing to zero said voltage deriving from said outputcircuit.

3. A system of sparkless make and break of a pair of contacts connectedin series with a current carrying electric circuit comprising: an

amplifier having an output circuit and an input circuit, means forcoupling said output circuit in voltage reducing relation with saidelectric circuit, and means coupling said input circuit with saidelectric circuit for applying to said amplifier for amplificationthereby a voltage proportional to current flowing in said electriccircuit.

4. In a system of sparkless commutation, a pair of co'mmutating contactsconnected in an electric circuit, an electronic control valve having ananode, a cathode and a control electrode, a transformer having a primaryand a secondary winding, means for connecting said primary Winding ofsaid transformer between said anode and cathode, means for connectingsaid secondary winding in series with said contacts in said circuit,means for applying between said grid and said cathode a potentialvarying as a function of potential between said contacts only while saidcontacts are in process of closing, and means for applying, between saidgrid and said cathode only while said contacts are opening a furtherpotential varying as a function of current flowing between saidcontacts.

5. A system of sparkless make and break of a pair of contacts connectedin series with a current carrying electric circuit comprising: anamplifier having an output circuit coupled in voltage inducing relationwith said electric circuit, said amplifier further comprising an inputcircuit coupled to said electric circuit for applying to said amplifierfor amplification thereby a voltage proportional to the potentialdifierence between said contacts.

6. A system of sparkless make and break of a pair of contacts connectedin series with a current carrying electric circuit comprising: anamplifier having an output circuit coupled in voltage inducing relationwith said electric circuit, said amplifier further comprising an inputcircuit coupled to said electric circuit for applying to said amplifierfor amplification thereby a voltage proportional to the current flowingbetween said pair of contacts.

7. In a system of commutation for making and then breaking a currentcarrying circuit: means for deriving the potential existing between twocommutating contacts connected in said current carrying circuit onlywhile said contacts are closing, said contacts when closed serving tocomplete said circuit, a feedback amplifier having an input circuit andan output circuit, means for applying said potential to said inputcircuit, means for coupling voltage deriving from said output circuit inseries with said current carrying circuit for opposing said differenceof potential and for reducing said difference of potential substantiallyto zero only while said contacts are closing, and means for thereafterclosing said contact and for reducing said voltage deriving from saidoutput circuit to zero after said contacts have been closed, means formeasuring the current flowing between said pair of commutating contactsonly while said contacts are in process of opening, a further feedbackamplifier having an input circuit and an output circuit,

means for applying to said input circuit of said further feedbackamplifier a potential proportional to said current flowing between saidpair of contacts while said contacts are in process of opening, meansfor couplin voltage derived from said output circuit of said furtherfeedback amplifier in series with said current carrying circuit forreducing said current flowing between said commutating contactssubstantially to zero while said contacts are in process of opening, andmeans for reducing to zero said voltage deriving from said outputcircuit after said commutating contacts have opened. 1

8. A system of sparkless commutation com prising: means for measuringthe potential existing between two commutating contacts connected in acurrent carrying circuit only while said contacts are closing, saidcontacts when closed serving to complete said circuit, said means formeasuring comprising an auxiliary contact connected to one of said twocommutating contacts via a high resistance, a feed-back amplifier havingan input circuit and an output circuit, means for connecting saidauxiliary contact to said input circuit to supply control potential tosaid input circuit, means for coupling voltage deriving from said outputcircuit in series with said current carrying circuit for opposing saiddifference of potential only while said contacts are closing, and meansfor thereafter closing said contacts and for reducing to zero saidvoltage deriving from said output circuit after said contacts have beenclosed.

9. A system of commutation of eiectric currents in an electric circuitby means of at least one brush and a plurality of commutator segments,comprising, first means for reducing to zero the voltage across saidcontacts only while said contacts are in process of closing byintroducing in said electric circuit only while said contacts areclosing a time varying voltage continuously equal and opposite to saidfirst voltage, second means for deriving said time varying voltage inresponse to a continuous measurement, while said contacts are closing,of resultant voltage across said contacts, third means for reducing tozero the current flowing between said contacts while said contacts arein process of opening by introducing in said electric circuit, onlywhile said contacts are in process of opening, a further time varyingvoltage continuously adjusted in amplitude in response to a continuousmeasurement of said current while said contacts are opening to reducesaid current substantially to zero, and mechanical switch means forsynchronizing the times of operation of said first and third means withrespect to relative motion of said at least one brush and said pluralityof commutator segments.

10. A system of commutation of electric currents in an electric circuitby means of at least one brush and a plurality of commutator segments,comprising, first means for reducing to zero the voltage across saidcontacts only while said contacts are in process of closing byintroducing in said electric circuit only while said contacts areclosing a time varying voltage continuously equal and opposite to saidfirst voltage, second means for deriving said time varying voltage inresponse to a continuous measurement, while said contacts are closing,of resultant voltage across said contacts, third means for reducing tozero the current flowing between said contacts while said contacts arein process of opening by introducing in said electric circuit, onlywhile said contacts are in process of opening, a further time varyingvoltage continuously adjusted in amplitude in response to a continuousmeasurement of said current while said contacts are opening to reducesaid current substantally to zero, and electronic switching means forsynchronizing the times of operation of said first and third means withrespect to relative motion ii of said at least one brushand saidpluralityof commutator segments.

11. In a: system of sparkless commutation, a firstcommutator segment, a.second commutator segment, means for synchronously moving, saidcommutator segments, a resistance interconnecting said commutatorsegments, a main current carrying brush contacting said firstcommutating segment, an auxiliary brush adjacent said main currentcarrying brush and contacting said first commutating segment, a.relatively high resistance: interconnecting said main current carryingbrushtand said auxiliary brush, a transformer secondary windin having afirst terminal, a low resistance connecting said current carrying brushto said first terminal, an electronic tube having an anode, a cathodeand a control electrode, a primary winding for. said transformersecondary winding and a source of anode voltage connected in seriesbetweensaid anode and cathode, an electrode only capacitively coupledwith said second. commutator segment, a resistance for connecting saidelectrode to said first terminal, a selector switch. having a pluralityof contacts and a selector arm, a first lead connecting one of saidcontacts with said first terminal, a second lead connecting. another ofsaid contacts with said auxiliary brush, a. third lead connecting stillanother of said contacts to said electrode, means coupling said selectorarm with said 1 control electrode, and meanscontroll'in motion. of saidselector arm relative to said contacts to provide contact betweensaidtselector arm with said one of said contacts. while said'maincurrent carrying brush'and said'first commutating segment are in processof breaking contact, and to provide contact between said. selector armand another of said contacts while said current carrying brush and saidfirst commutating segmentr are in process of making contact.

12.. In a system of sparkless commutation, a first commutator segment, asecond commutator segment, means for synchronously moving saidcommutator segments, a resistance interconnecting said commutatorsegments, a main current carrying brush contacting said firstcommutating segment, an auxiliary brush adjacent said main currentcarrying brush and contacting said first commutating segment, arelatively high resistance interconnecting said ,main'current carryingbrush and said. auxiliary brush, a transformer secondary winding havinga first terminal, a low resistance connecting said current carryingbrush to said, first terminal, an electronic tube having an anode, acathode and a control electrode, a primary winding for said transformersecondary winding and a source of anode voltage connected in seriesbetween said anode and cathode, an electrode only capacitively coupledwith said second commutator segment, means for connectingsaid electrodeto said first terminal, a plurality of electronic switching channels,each of said channels having an output circuit, means coupling all saidoutput circuits in control relation to said control electrode, each ofsaid plurality of electronic switching channels further comprising aseparate electronic tube having a first and a second control grid, meansfor applying sequential on-switching voltages to said first controlgrids, means for connecting one of said second control grids to saidauxiliary brush, means for connecting another of said second controlelectrodes to said first terminal, and means for synchronizing saidon-switching voltages with relative motion of said commutator segments.

13. In a system of sparkless commutation, a pair of commutating contactsconnected in an electric circuit, an electronic control valve havin ananode, a cathode and a control eletrode, a transformer having. a primaryand a second.- ary Winding, means for connecting said primary winding ofsaid transformer between said anode and cathode, means .for connectingsaid secondary widing in series with said contacts in said circuit,means comprising an electronic switching tube for applying between saidgrid and said cathode a potential varying as a function of potentialbetween said contacts only while said contacts are in process ofclosing, and means. comprising a further electronic switchingtube forapplying between said grid and said cathode only While said contacts areopening a further potential varying as a function of currentflowingbetween said contacts.

PIERRE MARIE GABRIEL TOULON.

' No references cited.

